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Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Details) | 3 Months Ended
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Mar. 31, 2016 | Mar. 31, 2015
Reclassifications Out of Accumulated Other Comprehensive Income (Loss) [Abstract] |  |
Reclassifications Out of Accumulated Other Comprehensive Income | not material | not material

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- Definition Reclassifications Out of Accumulated Other Comprehensive Income (Loss) [Abstract] + References No definition available. + Details
Name: | ale_ReclassificationsOutofAccumulatedOtherComprehensiveIncomeLossAbstract
Namespace Prefix: | ale_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Statement of whether reclassifications out of accumulated other comprehensive income (loss) were material for the period presented. + References No definition available. + Details
Name: | ale_ReclassificationsOutofAccumulatedOtherComprehensiveIncomeLossMateriality
Namespace Prefix: | ale_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration